Caldwell, who turns 59 Thursday, is leaving the positions of quarterback coach and offensive coordinator for the Baltimore Ravens to take over the Detroit coaching opening, the Lions said Tuesday.
Caldwell accepted the Detroit job one day after Ken Whisenhunt took the coaching job at Tennessee. Whisenhunt, a former Arizona Cardinals head coach and, until Monday, the offensive coordinator at San Diego, was reportedly a top choice for the opening in Detroit.
The Lions' head coaching job became available when Jim Schwartz was fired Dec. 30. Schwartz was 29-51 in five seasons in Detroit. The Lions were 7-9 in 2013.
Caldwell had been quarterbacks coach and assistant head coach at Indianapolis and was promoted to head coach when Tony Dungy resigned after the 2008 season. Indianapolis went to the Super Bowl after going 14-2 in the regular season in Caldwell's first season.
The Colts were 10-6 the next year and 2-14 in 2011, which was the season quarterback Peyton Manning missed because of neck surgery. Caldwell was fired after that season, which left him with a 26-22 NFL coaching record.
He served as the offensive coordinator for Baltimore for two seasons, including the Super Bowl-winning 2012 team. He was part of Dungy's staff when the Colts won the Super Bowl after the 2006 season.
Caldwell also served eight seasons as head coach for Wake Forest, going 26-63 but gaining an Aloha Bowl berth in 1999.